Field
Aspects of the present invention mainly relate to an image forming apparatus, such as a copying machine or a printer adopting an electrophotographic method or an electrostatic storage method, a method for controlling the amount of light, and a method for controlling the image forming apparatus, and particularly relates to a method for detecting the amount of misregistration and the amount of variation in density of each color developer formed on an image bearing member or an intermediate transfer member.
Description of the Related Art
Color image forming apparatuses including a plurality of photosensitive drums are currently designed to suppress misregistration of an image of each color, but due to a mechanical installation error of each photosensitive drum, an optical path length error of a laser beam of each color, a change in each optical path, and the like, misregistration occurs between the images. For this reason, a method for correcting the misregistration between the images is needed. In addition, because the density of each image varies due to conditions such as a use environment and the number of sheets printed, and accordingly color balance (so-called “tone”) varies, a method for correcting the density of each image is needed. As a method for correcting the amount of misregistration and the amount of variation in density of each image, for example, the following method is disclosed in Japanese Patent Laid-Open No. 05-249787. That is, a method is disclosed in which toner patterns are formed on an image bearing member and an optical sensor including light-emitting devices and light-receiving devices detects the formed toner patterns. The amount of misregistration and the amount of variation in density of each image are then calculated and corrected.
In addition, for example, in Japanese Patent Laid-Open No. 2000-039746, a method for controlling the amount of light emitted by light-emitting devices of an optical sensor is disclosed. When detecting toner patterns, the optical sensor receives diffuse reflection light and specular reflection light. The amount of light received by the optical sensor and an output voltage of the optical sensor that has performed photoelectric conversion on the received light vary depending on various factors. The optical sensor therefore detects the toner patterns transferred onto an image bearing member or an intermediate transfer member, and the amount of light, which is emitted by the optical sensor, necessary to obtain a desired amount of light received is calculated based on the amount of light received and the amount of light emitted by the light-emitting devices obtained during the detection. The desired amount of light received or output voltage can thus be detected by controlling the light-emitting devices of the optical sensor in such a way as to achieve the calculated amount of light. Furthermore, for example, in Japanese Patent Laid-Open No. 2009-93155, a configuration is disclosed in which, when toner patterns are detected using an intermediate transfer belt, toner patterns of color developers are used as bases and a toner pattern of a black developer is superimposed upon the toner patterns of the color developers.
In these examples of the related art, in order to calculate an optimal amount of light emitted by light-emitting devices, toner patterns need to be transferred onto an intermediate transfer member, and an optical sensor needs to detect the toner patterns. That is, in an image forming apparatus, it takes some time to remove the toner patterns from the intermediate transfer member after performing an initial operation before the transfer of the toner patterns, transferring the toner patterns onto the intermediate transfer member, and detecting the toner patterns using the optical sensor. This period of time is a waiting time of a user. In addition, if, as in the examples of the related art, an optical sensor that detects diffuse reflection light detects toner patterns transferred onto a surface of an intermediate transfer member whose diffuse reflectance is high, a difference between an output for the toner patterns and an output for the surface of the intermediate transfer member is small, thereby decreasing a signal-to-noise (SN) ratio of a sensor output. If the SN ratio of the sensor output decreases, erroneous detection of the toner patterns might occur when noise is caused by a stain on the surface of the intermediate transfer member, variation in the amount of toner transferred at an end of a toner pattern, or the like. In this case, it is difficult to detect the toner pattern reliably and accurately.